1. Field of the Invention
The present invention relates to tantalum chip capacitors. More particularly, though not exclusively, the present invention relates to improved tantalum chip capacitors and methods for manufacturing the same.
2. Problems in the Art
Capacitors exist in the art which are made from a capacitive element such as a tantalum slug or pellet. To create a conventional tantalum slug, tantalum powder is pressed with a binder and then exposed to a process for forming a polarized capacitor having a positive end and a negative end. A typical tantalum slug will have an anode comprised of a wire extending from the slug and a cathode comprised of a conductive surface formed at the opposite side of the tantalum slug.
Some prior art tantalum capacitors are formed by cutting the anode wire and covering the anode and cathode ends of the capacitor with a conductive material. This results in a nib or bump that sticks out of the package, increasing the size and non-uniformity of the part. The electrical contact between the tantalum wire and the conductive material is through the sides of the tantalum wire, therefore requiring this nib.
Other prior art tantalum slugs are fitted with external leads which are comprised of discrete pieces of metal attached to the anode and cathode of the capacitive element. Users of such tantalum capacitors desire to attach the capacitors to a circuit board using reflow solder. As a result, terminations are required which are suitable to be attached to a circuit board using reflow solder. Prior art tantalum capacitors fitted with such external leads have been produced in various ways. Some prior art capacitors are made using a lead frame providing connection terminals where the tantalum slug is placed within a lead frame. An electrical connection is made between the anode and cathode and one of the connection terminals. Other prior art tantalum capacitors use a flat metal piece which is directly connected to the anode lead of the tantalum slug. The excess portions of the anode leads can be sheared off so that the flat metal piece provides a surface for use as an anode terminal. Other prior art tantalum slugs are disposed within metal channels which form anode and cathode terminals. The anode lead wire of the tantalum slug can be welded to the metal channel to form an electrical connection. Other prior art tantalum slugs simply have discrete metal terminals which are fixed to the ends of the tantalum slug and which make electrical contact to the anodes and cathodes of the tantalum slug. Still other prior art tantalum slugs are processed with a flat piece of tantalum metal being substituted for the tantalum wire at the anode end, and with a similar flat piece of metal being attached to the opposing cathode end, and with both pieces of metal being further metallized on their external faces so as to provide solderable surfaces.
It is known in other fields of technology to use thin film metallization methods such as sputtering to coat the ends of devices such as chip resistors.
It can therefore be seen that there is a need for an improved tantalum chip capacitor and method for making the same.
A general feature of the present invention is the provision of an improved tantalum chip capacitor and a method for making the same which overcomes problems found in the prior art.
A further feature of the present invention is the provision of an improved tantalum chip capacitor and a method for making the same in which the cross sectional surface of the tantalum wire is metallized at the point of egress from the insulating package creating a conformal, uniformly shaped device.
A further feature of the present invention is the provision of a method of making an improved tantalum chip capacitor which includes a step of cutting or grinding the tantalum wire such that the finished product does not include a protrusion caused by the tantalum wire or that such protrusion is negligible.
Further features, objects, and advantages of the present invention include:
An improved tantalum chip capacitor and method which results in improved utilization of available package volume, specifically, such that a larger portion of the available package volume may be occupied by the tantalum capacitor element.
An improved tantalum chip capacitor and method which results in improved handleability through the elimination of the protruding tantalum wire and more consistent package dimensions and shapes.
An improved tantalum chip capacitor and method which results in improved electrical stability of the capacitor including the equivalent series resistance (ESR) of the capacitor.
An improved tantalum chip capacitor and method which results in improved manufacturability and a reduced manufacturing cost.
An improved tantalum chip capacitor and method resulting from the use of thin film processes to create terminations on the capacitor and from avoiding the use of discrete pieces of metal to create such terminations.
An improved tantalum chip capacitor and method which utilizes vacuum processes such as sputtering or evaporation to create terminations on the capacitor.
These as well as other objects features and advantages of the present invention will become apparent from the following specification and claims.
The tantalum chip capacitor of the present invention includes a tantalum element with an insulating material surrounding at least a portion of the element. A tantalum wire is electrically connected to the tantalum element and extends through the insulating material. The tantalum wire is cut or ground at the point of egress from the insulating material such that the exposed surface of the wire is substantially flush with the insulating material and is electrically connected to a first terminal which is substantially flat in the proximity of the wire. The second end of the tantalum element is electrically connected to a second terminal.
The tantalum chip capacitors of the present invention can be created by a number of methods. A first method for creating the tantalum chip capacitor of the present invention includes the steps of grinding the second end of the element to expose a conductive surface, applying a conductive material to both ends of the capacitor element where terminations are desired, cutting or grinding the first end of the capacitor element so that the terminal wire becomes substantially flush with the first end creating a flush surface on the first end, applying a conductive material to the first end of the element, and applying termination materials to both ends to create terminations. A second method of creating the tantalum chip capacitors of the present invention includes the steps of cutting or grinding the first end of the capacitor element so that the end of the wire is substantially flush with the first end of the element, applying a conductive material to the surfaces of the capacitor element, masking the first and second ends of the element where terminations are desired, removing the unmasked conductive material, removing the masks, and applying termination materials to the first and second ends to create terminations.
A third method comprises making the terminal wire flush with the first end of the capacitor chip element and applying a conductive material to the first and second ends of the capacitor chip element where terminations are desired. A further embodiment of this third method includes arranging a plurality of capacitor chip elements in a grid with the first and second ends of the capacitor elements exposed and the side surfaces masked by adjacent capacitor elements, and applying conductive material to the exposed first and second ends of the capacitor elements where terminations are desired.